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Abstract:

The present invention provides an excellent optical pressure-sensitive
adhesive sheet having an excellent adhesion property to an optical
member. The present invention relates to an optical pressure-sensitive
adhesive sheet comprising a pressure-sensitive adhesive layer, wherein a
relative dielectric constant at a frequency of 1 MHz is 5 to 10, and an
adhesion strength to a glass, which is measured with a peel angle of
180° and a tensile speed of 300 mm/min after 30 min of laminating
the optical pressure-sensitive adhesive sheet to the glass, is 3 N/20 mm
to 15 N/20 mm.

Claims:

1. An optical pressure-sensitive adhesive sheet comprising a
pressure-sensitive adhesive layer, wherein a relative dielectric constant
at a frequency of 1 MHz is 5 to 10, and an adhesion strength to a glass,
which is measured with a peel angle of 180.degree. and a tensile speed of
300 mm/min after 30 min of laminating the optical pressure-sensitive
adhesive sheet to the glass, is 3 N/20 mm to 15 N/20 mm.

3. The optical pressure-sensitive adhesive sheet according to claim 2,
wherein the acrylic pressure-sensitive adhesive layer comprises, as a
base polymer, an acrylic polymer formed from a component comprising, as
an essential monomer component, alkyl ester(meth)acrylate having a
straight-chain or branched alkyl group having 1 to 14 carbon atoms and/or
alkoxyalkyl ester(meth)acrylate.

4. The optical pressure-sensitive adhesive sheet according to claim 3,
wherein the acrylic polymer is formed by an active-energy-ray
polymerization method with an irradiation of an active-energy-ray.

Description:

[0004] Recently, display devices such as liquid crystal displays (LCDs) or
input devices, such as a touch panel, which is used by combining the
display device has been widely used in various fields. In manufacturing
the display devices or the input devices, a pressure-sensitive adhesive
sheet is used for laminating optical members (see, for example, Patent
Document 1).

[0005] A touch panel has been considered as a trend of an image display
method, and in particular, an electric capacity type touch panel has been
widely used. The electric capacity type touch panel has a configuration
in which many members are laminated, and a pressure-sensitive adhesive
sheet is used for the purpose of laminating the members. An example of
the electric capacity type touch panel may include an electric capacity
type touch panel having a laminated structure of cover
glass/pressure-sensitive adhesive sheet/conductive film such as an indium
tin oxide film (ITO film)/glass substrate.

[0006] The electric capacity type touch panel has a structure in which,
when the touch panel is touched by a finger, the capacitance of the
corresponding position is changed, and detection (sensing) is performed
when the amount of the capacitance changed exceeds a predetermined
critical value. In the touch panel having a laminated structure of cover
glass/pressure-sensitive adhesive sheet/conductive film (ITO film)/glass
substrate, the capacitance changed by touching the panel with a finger
needs to be transmitted to a detection part (sensing part) of the touch
panel (T/P). Accordingly, the pressure-sensitive adhesive sheet used in
the electric capacity type touch panel needs to have high relative
dielectric constant. Meanwhile, if relative dielectric constant of the
pressure-sensitive adhesive sheet is too high, noise tends to be easily
detected, and in the case where an output signal is changed, the
transmission time of a signal tends to be delayed, thereby causing a
problem in detection sensitivity (sensing sensitivity).

[0007] The pressure-sensitive adhesive sheet used in the electric capacity
type touch panel needs to have an excellent adhesion property to members
constituting the touch panel. For example, the pressure-sensitive
adhesive sheet used in the electric capacity type touch panel having a
laminated structure of cover glass/pressure-sensitive adhesive
sheet/conductive film (ITO film)/glass substrate needs to have an
excellent adhesion property, particularly, to a cover glass. [0008]
Patent Document 1: JP 2002-363523 A

SUMMARY OF THE INVENTION

[0009] The present invention has been made in an effort to provide an
excellent optical pressure-sensitive adhesive sheet having an excellent
adhesion property to an optical member. Particularly, the present
invention provides an optical pressure-sensitive adhesive sheet that,
when the optical pressure-sensitive adhesive sheet is used in laminating
members constituting the electric capacity type touch panel, exhibits an
excellent adhesion property to the members constituting the touch panel,
and does not negatively affect the performance of the touch panel such as
a detection sensitivity or a response speed.

[0010] The present inventors have intensively studied in order to solve
the problems. As a result, the inventors have found out that an excellent
optical pressure-sensitive adhesive sheet exhibiting an excellent
adhesion property to optical members can be obtained by setting relative
dielectric constant at a frequency of 1 MHz and adhesion force to glass
within a specific range. Particularly, the present inventors have found
out an excellent optical pressure-sensitive adhesive sheet that, when the
optical pressure-sensitive adhesive sheet is used in laminating members
constituting the electric capacity type touch panel, exhibits an
excellent adhesion property to members constituting the touch panel, and
does not negatively affect the performance of the touch panel such as a
detection sensitivity or a response speed, thereby completing the present
invention.

[0011] That is, the optical pressure-sensitive adhesive sheet of the
present invention comprises a pressure-sensitive adhesive layer, wherein
a relative dielectric constant at a frequency of 1 MHz is 5 to 10, and an
adhesion strength to a glass, which is measured with a peel angle of
180° and a tensile speed of 300 mm/min after 30 min of laminating
the optical pressure-sensitive adhesive sheet to the glass, is 3 N/20 mm
to 15 N/20 mm.

[0013] In the optical pressure-sensitive adhesive sheet of the present
invention, the acrylic pressure-sensitive adhesive layer preferably
comprises, as a base polymer, an acrylic polymer formed from a component
comprising, as an essential monomer component, alkyl ester(meth)acrylate
having a straight-chain or branched alkyl group having 1 to 14 carbon
atoms and/or alkoxyalkyl ester(meth)acrylate.

[0014] In the optical pressure-sensitive adhesive sheet of the present
invention, the acrylic polymer is preferably formed by an
active-energy-ray polymerization with an irradiation of an
active-energy-ray.

[0016] In the optical pressure-sensitive adhesive sheet of the present
invention, a total light transmittance is preferably 90% or more and a
haze is preferably 3.0% or less.

[0017] The optical pressure-sensitive adhesive sheet of the present
invention is preferably used for laminating to a member contained in a
touch panel.

[0018] In the optical pressure-sensitive adhesive sheet of the present
invention, the touch panel is preferably an electric capacity type touch
panel.

[0019] In addition, in a liquid crystal display device or an input device
of the present invention comprises the optical pressure-sensitive
adhesive sheet.

[0020] Since the optical pressure-sensitive adhesive sheet according to
the present invention has the above configuration, the optical
pressure-sensitive adhesive sheet has an excellent adhesion property to
optical members. In particular, when the optical pressure-sensitive
adhesive sheet according to the present invention is used for laminating
members constituting the electric capacity type touch panel, the optical
pressure-sensitive adhesive sheet exhibits an excellent adhesion property
to the members constituting the touch panel, and does not negatively
affect the performance of the touch panel such as a detection sensitivity
or a response speed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a schematic view illustrating an embodiment of an
electric capacity type touch panel formed by laminating members using an
optical pressure-sensitive adhesive sheet according to the present
invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] In the optical pressure-sensitive adhesive sheet according to the
present invention, a relative dielectric constant at a frequency of 1 MHz
is 5 to 10, and an adhesion strength to glass (which is measured with a
release angle of 180° and tensile speed of 300 mm/min after 30
minutes of laminating the pressure-sensitive adhesive sheet to the glass)
is 3 N/20 mm to 15 N/20 mm. In the present specification, the "relative
dielectric constant at a frequency of 1 MHz" may be simply referred to
"relative dielectric constant", and the adhesion strength to glass may be
referred to "adhesion force to glass".

[0023] The optical pressure-sensitive adhesive sheet according to the
present invention has at least a pressure-sensitive adhesive layer and
includes any forms such as a tape and a sheet. The pressure-sensitive
adhesive sheet according to the present invention may be a substrateless
type pressure-sensitive adhesive sheet that does not have substrate
(substrate layer), or a pressure-sensitive adhesive sheet with substrate
(substrate layer). Particularly, the pressure-sensitive adhesive sheet
according to the present invention is preferably a substrateless type
pressure-sensitive adhesive sheet formed only with a pressure-sensitive
adhesive layer from the standpoint of improving optical properties such
as thinning and transparency. The "substrate" does not include a release
liner (separator).

[0024] The optical pressure-sensitive adhesive sheet according to the
present invention may be a single-sided pressure-sensitive adhesive sheet
having a pressure-sensitive adhesive property on one side thereof or a
double-sided pressure-sensitive adhesive sheet having an
pressure-sensitive adhesive property on both sides thereof. The
pressure-sensitive adhesive layer providing an pressure-sensitive
adhesive surface may be a single layer structure or a laminate structure.

[0025] In the optical pressure-sensitive adhesive sheet according to the
present invention, a relative dielectric constant at a frequency of 1 MHz
is 5 to 10, preferably 5 to 9, and more preferably 5 to 8. If the
relative dielectric constant is more than 10 or the relative dielectric
constant is less than 5, the optical members to which the
pressure-sensitive adhesive sheet is applied, may have damaged functions
or characteristics thereof. The relative dielectric constant may be
determined according to JIS K 6911.

[0026] For example, in the case where the optical pressure-sensitive
adhesive sheet according to the present invention is applied to the
electric capacity type touch panel, if the relative dielectric constant
is less than 5, the capacitance value required for detecting (sensing)
the touch panel is decreased, thereby being easily affected by a noise
signal, and the ratio of a signal of detection and noise is decreased,
thereby easily causing misoperation, which is not preferable. Meanwhile,
if the relative dielectric constant is more than 10, the capacitance
value becomes too large, thereby easily causing a time delay in signal
and decreasing the sensitivity of detection, which is not preferable.

[0027] In the optical pressure-sensitive adhesive sheet according to the
present invention, the adhesion force to glass is 3 N/20 mm to 15 N/20
mm, preferably 5 N/20 mm to 15 N/20 mm, and more preferably 7 N/20 mm to
15 N/20 mm. When the adhesion force to glass is more than 15 N/20 mm,
rework (amendment of position) may not be able to be performed.
Meanwhile, when the adhesion force to glass is less than 3 N/20 mm, a
problem may occur from the standpoint of adhesion reliability.

[0028] The adhesion force to glass may be obtained by laminating the
pressure-sensitive adhesive sheet to the glass plate, being left standing
them for 30 min, and then releasing the pressure-sensitive adhesive sheet
from the glass plate under the environment of 23° C. and 50% RH
and under the conditions of a release angle of 180° and a tensile
speed of 300 mm/min. In the glass plate, an adherend surface (surface to
which the pressure-sensitive adhesive sheet is adhered) is a surface from
which fluorescence is not emitted even when irradiating UV having a
wavelength of 254 nm by a UV lamp. In the case where the
pressure-sensitive adhesive sheet is a double-sided pressure-sensitive
adhesive sheet, a backing material (e.g., PET film having a thickness of
25 μm) is limited thereto, and the adhesion force is measured.
Examples of the glass plate include particularly a slide glass, and
examples of the slide glass include "MATUNAMI MICRO SLIDE GLASS S series,
manufactured by Matsunami Glass Ind., Ltd.". The adhesion force to glass
means a force when the pressure-sensitive adhesive sheet adhered to the
glass plate is released from the glass plate.

[0029] In the optical pressure-sensitive adhesive sheet according to the
present invention, a total light transmittance (in accordance with JIS K
7361) in a visible light wavelength range is not particularly limited,
but is preferably 90% or more (e.g., 90% to 99.9%), and more preferably
91% or more (e.g., 91% to 99.9%). In the pressure-sensitive adhesive
sheet according to the present invention, a haze (in accordance with JIS
K 7136) is not particularly limited, but is preferably 3.0% or less
(e.g., 0.1% to 3.0%), and more preferably 2.0% or less (e.g., 0.1% to
2.0%). This is because that it is preferable that the optical
pressure-sensitive adhesive sheet according to the present invention has
a high transparency from the standpoint of visibility in the case where
the pressure-sensitive adhesive sheet is applied to the optical members,
such as a case where the pressure-sensitive adhesive sheet is applied to
the electric capacity type touch panel. The total light transmittance and
haze can be measured using, for example, a haze meter (trade name of
`HM-150` manufactured by Murakami Color Research Laboratory Co., Ltd.).

[0030] (Pressure-Sensitive Adhesive Layer)

[0031] The optical pressure-sensitive adhesive sheet according to the
present invention has at least a pressure-sensitive adhesive layer. The
pressure-sensitive adhesive layer is formed from a pressure-sensitive
adhesive composition. As described below, it is preferable that the
pressure-sensitive adhesive sheet according to the present invention has
an acrylic pressure-sensitive adhesive layer as the pressure-sensitive
adhesive layer. Meanwhile, this acrylic pressure-sensitive adhesive layer
is formed from an acrylic pressure-sensitive adhesive composition. The
"pressure-sensitive adhesive composition" includes both meanings of a
"composition for forming the pressure-sensitive adhesive layer" and a
"composition for forming the pressure-sensitive adhesive".

[0033] Acrylic pressure-sensitive adhesives or polyether-based
pressure-sensitive adhesives are preferably used as the
pressure-sensitive adhesive from the standpoint of transparency,
processability, and durability, and the acrylic pressure-sensitive
adhesives are more preferably used. Namely, the optical
pressure-sensitive adhesive sheet according to the present invention
preferably has an acrylic pressure-sensitive adhesive layer or a
polyether-based pressure-sensitive adhesive layer, and more preferably
has an acrylic pressure-sensitive adhesive layer.

[0034] The content of the base polymer in the pressure-sensitive adhesive
layer is not particularly limited, but is preferably 60 wt % or more
(e.g., 60 wt % to 100 wt %), and more preferably 80 wt % or more (e.g.,
80 wt % to 100 wt %) based on the total weight of the pressure-sensitive
adhesive layer.

[0035] The base polymer is prepared by polymerizing monomer components by
a known/general polymerization method. For example, the acrylic polymer
that is the base polymer of the acrylic pressure-sensitive adhesive is
formed by a polymerization method such as a solution polymerization
method, an emulsion polymerization method, a bulk polymerization method
and a polymerization method by active-energy-ray irradiation (an
active-energy-ray polymerization method or a photopolymerization method).

[0036] The polyether-based pressure-sensitive adhesive layer includes a
polyether-based polymer as a base polymer. The polyether-based polymer is
not particularly limited, and a polyoxyalkylene-based polymer is
preferable.

[0037] The polyoxyalkylene-based polymer is not particularly limited, and
the polyoxyalkylene-based polymer preferably has a repeating unit
represented by the following general formula (1) in a main chain of the
polymer.

--R1--O-- [0038] (wherein R' is an alkylene group)

[0039] In the general formula (I), R1 is preferably a straight-chain
or branched alkylene group having 1 to 14 carbon atoms, and more
preferably a straight-chain or branched alkylene group having 2 to 4
carbon atoms.

[0040] Specific examples of the repeating unit represented by the general
formula (I) include --CH2O--, --CH2CH2O--,
--CH2CH(CH3)O--, --CH2CH(CH2H5)O--,
--CH2C(CH3)2O-- and --CH2CH2CH2CH2O--.
The backbone of main chains of the polyoxyalkylene-based polymer may
consist of only one type of repeating unit or two or more types of
repeating units. Particularly, polymers having --CH2CH(CH3)O--
as a main repeating unit are preferable from the standpoint of
availability and workability. Also, polymers having repeating units other
than an oxyalkylene group may be included in the main chain thereof,
wherein the sum of oxyalkylene units in the polymer is preferably 80 wt %
or more, and more preferably 90 wt % or more, based on the total amount
(100 wt %) of the monomer component forming the polymer.

[0041] A polyoxyalkylene-based polymer may be a straight-chain polymer, a
branched polymer, or a mixture thereof, and the polyoxyalkylene-based
polymer may include 50 wt % or more of the straight-chain polymer in
order to obtain good pressure-sensitive adhesion.

[0042] The acrylic pressure-sensitive adhesive layer contains an acrylic
polymer as a base polymer. The acrylic polymer includes an acrylic
monomer as an essential monomer component. The acrylic polymer may be a
homopolymer of the acrylic monomer, a copolymer of a plurality of acrylic
monomers, or a copolymer of the acrylic monomer and monomer other than
the acrylic monomer.

[0043] The acrylic monomer is preferably alkyl ester(meth)acrylate having
a straight-chain or branched alkyl group or alkoxyalkyl
ester(meth)acrylate. The term "(meth)acryl" represents "acryl" and/or
"methacryl" and the same applies to others.

[0044] As the acrylic monomer, alkyl ester(meth)acrylate having a
straight-chain or branched alkyl group may be used alone, alkoxyalkyl
ester(meth)acrylate may be used alone, or alkyl ester(meth)acrylate
having a straight-chain or branched alkyl group and alkoxyalkyl
ester(meth)acrylate may be used in combination. In the case where alkyl
ester(meth)acrylate having a straight-chain or branched alkyl group and
alkoxyalkyl ester(meth)acrylate are used in combination as the acrylic
monomer, a content thereof is not particularly limited.

[0045] In the optical pressure-sensitive adhesive sheet according to the
present invention, alkoxyalkyl ester(meth)acrylate is preferably used as
the acrylic monomer from the standpoint of increasing relative dielectric
constant while obtaining a desired adhesion force to glass while.

[0046] The alkyl ester(meth)acrylate having a straight-chain or branched
alkyl group is not particularly limited, and examples thereof include
alkyl ester(meth)acrylate of which an alkyl group has 1 to 20 carbon
atoms such as methyl(meth)acrylate, ethyl(meth)acrylate,
propyl(meth)acrylate, isopropyl(meth)acrylate, butyl(meth)acrylate,
isobutyl(meth)acrylate, s-butyl(meth)acrylate, t-butyl(meth)acrylate,
pentyl(meth)acrylate, isopentyl(meth)acrylate, hexyl(meth)acrylate,
heptyl(meth)acrylate, octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,
isooctyl(meth)acrylate, nonyl(meth)acrylate, isononyl(meth)acrylate,
decyl(meth)acrylate, isodecyl(meth)acrylate, undecyl(meth)acrylate,
dodecyl(meth)acrylate, tridecyl(meth)acrylate, tetradecyl(meth)acrylate,
pentadecyl(meth)acrylate, hexadecyl(meth)acrylate,
heptadecyl(meth)acrylate, octadecyl(meth)acrylate,
nonadecyl(meth)acrylate, and eicosyl(meth)acrylate. Among alkyl
ester(meth)acrylates, alkyl ester(meth)acrylate having the straight-chain
or branched alkyl group is preferably alkyl ester(meth)acrylate having a
straight-chain or branched alkyl group having 1 to 14 carbon atoms, and
more preferably alkyl ester(meth)acrylate having a straight-chain or
branched alkyl group having 1 to 10 carbon atoms. The alkyl
ester(meth)acrylate having a straight-chain or branched alkyl group may
be used either alone or in combination of two or more thereof.

[0048] In the acrylic polymer, there is no particular limit to the content
of the sum of alkyl ester(meth)acrylate having a straight-chain or
branched alkyl group and the alkoxyalkyl ester(meth)acrylate in the total
monomer components (100 wt %) forming the acrylic polymer. However, from
the standpoint of easily controlling the adhesion property and relative
dielectric constant of the pressure-sensitive adhesive sheet, the content
is preferably 70 wt % or more (e.g., 70 wt % to 100 wt %) and more
preferably 80 wt % or more (e.g., 80 wt % to 100 wt %) based on the total
amount of the monomer components (100 wt %) forming the acrylic polymer.

[0049] In the case where the alkoxyalkyl ester(meth)acrylate is used as
the acrylic monomer, the content of alkoxyalkyl ester(meth)acrylate in
the total monomer component (100 wt %) forming the acrylic polymer is
preferably 40 wt % or more, and more preferably 50 wt % or more from the
standpoint of easily obtaining a pressure-sensitive adhesive sheet having
a good adhesion property to optical members and a high relative
dielectric constant.

[0050] The acrylic polymer may be a copolymer of alkyl ester(meth)acrylate
having a straight-chain or branched alkyl group and/or alkoxyalkyl
ester(meth)acrylate and a copolymerizable monomer. The copolymerizable
monomer is not particularly limited, and examples thereof include polar
group-containing monomers, multifunctional monomers and other
copolymerizable monomers. The copolymerizable monomers are used either
alone or in combination of two or more thereof.

[0051] Examples of the polar group-containing monomers include: carboxyl
group-containing monomers such as (meth)acrylate, itaconic acid, maleic
acid, fumaric acid, crotonic acid and anhydrides thereof (e.g., maleic
anhydride); hydroxyl group-containing monomers such as vinyl alcohol,
aryl alcohol, and hydroxyalkyl(meth)acrylate such as
2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate,
4-hydroxybutyl(meth)acrylate and 6-hydroxyhexyl(meth)acrylate; amide
group-containing monomers such as (meth)acrylamide,
N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide,
N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide and
N-hydroxyethyl acrylamide; amino group-containing monomers such as
aminoethyl(meth)acrylate, dimethylaminoethyl(meth)acrylate and t-butyl
aminoethyl(meth)acrylate; glycydyl group-containing monomers such as
glycidyl(meth)acrylate and methylglycidyl(meth)acrylate; cyano
group-containing monomers such as acrylonitrile and methacrylonitrile;
heterocyclic ring-containing vinyl monomers such as N-vinyl pyridine,
N-vinyl piperidone, N-vinyl pyrimidine, N-vinyl piperazine, N-vinyl
pyrrole, N-vinyl imidazole and N-vinyl oxazole in addition to
N-vinyl-2-pyrrolidone and (meth)acryloyl morpholine; sulfonate
group-containing monomers such as sodium vinyl sulfonate; phosphate
group-containing monomers such as 2-hydroxyethyl acryloyl phosphate;
imide group-containing monomers such as cyclohexyl maleimide and
isopropyl maleimide; and isocyanate group-containing monomers such as
2-methacryloyloxyethyl isocyanate. The polar group-containing monomers
are used either alone or in combination of two or more thereof.

[0052] Among the examples thereof, as the polar group-containing monomer,
a hydroxyl group-containing monomer is preferable, and a hydroxyl
group-containing monomer such as 2-hydroxyethyl(meth)acrylate, and
4-hydroxybutyl(meth)acrylate is more preferable from the standpoint of
obtaining a desired adhesion property and increasing a relative
dielectric constant in the pressure-sensitive adhesive sheet.

[0053] In the pressure-sensitive adhesive layer of the pressure-sensitive
adhesive sheet, if carboxyl group-containing monomers such as acrylic
acid or anhydrides thereof are used as the monomer component forming the
acrylic polymer as the base polymer, the relative dielectric constant of
the pressure-sensitive adhesive sheet may be decreased.

[0054] In the case where the optical pressure-sensitive adhesive layer
according to the present invention has the acrylic pressure-sensitive
adhesive layer, it is preferable that the acrylic polymer of the acrylic
pressure-sensitive adhesive layer does not substantially contain a
carboxyl group-containing monomer (particularly, acrylic acid), as a
monomer component forming the polymer. The wording "does not
substantially contain a carboxyl group-containing monomer (particularly,
acrylic acid)" means that the carboxyl group-containing monomer is
contained in an amount of less than 1 wt % (preferably less than 0.1 wt
%) based on the total amount (100 wt %) of the monomer component forming
the acrylic polymer.

[0055] The content of the polar group-containing monomer is not
particularly limited, but is preferably 5 wt % to 50 wt %, and more
preferably 10 wt % to 40 wt % based on the total monomer components
forming the acrylic polymer (100 wt %).

[0056] Particularly, the content of the hydroxyl group-containing monomer
such as 2-hydroxyethyl(meth)acrylate, and 4-hydroxybutyl(meth)acrylate is
preferably 5 wt % to 50 wt %, and more preferably 10 wt % to 40 wt %
based on the total amount of the monomer components forming the acrylic
polymer (100 wt %). If the content of the hydroxyl group-containing
monomer is more than 50 wt %, the pressure-sensitive adhesive layer
becomes hard, and there may be a problem in that the adhesion property of
the pressure-sensitive adhesive sheet is decreased. Meanwhile, if the
content of the hydroxyl group-containing monomer is less than 5 wt %,
there may be a problem in that the pressure-sensitive adhesive layer
undergoes white turbidity upon humidification.

[0058] In the total monomer component forming the acrylic polymer, the
content of the multifunctional monomer is not particularly limited, but
is preferably 5 wt % or less (e.g., 0.01 wt % to 5 wt %), and more
preferably 1 wt % or less (e.g., 0.01 wt % to 1 wt %) based on the total
amount of the monomer component forming the acrylic polymer (100 wt %).
If the contents of the multifunctional monomers are excessively high,
cohesion force of the pressure-sensitive adhesive layer may be
excessively increased and the stress relaxation properties may be
lowered.

[0059] As the copolymerizable monomers other than the polar
group-containing monomers and multifunctional monomers as described above
(other copolymerizable monomers), examples thereof include: alkyl
ester(meth)acrylate having a cyclic alkyl group such as
cyclopentyl(meth)acrylate, cyclohexyl(meth)acrylate and
isobornyl(meth)acrylate; ester(meth)acrylate other than the
above-mentioned alkyl ester(meth)acrylate such as ester(meth)acrylate
having aromatic hydrocarbon groups such as phenyl(meth)acrylate, polar
group-containing monomers and polyfunctional monomers; vinyl esters such
as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as
styrene and vinyl toluene; olefins or dienes such as ethylene, butadiene,
isoprene, and isobutylene; vinyl ethers such as vinyl alkyl ether; and
vinyl chloride.

[0060] Among the examples thereof, alkyl ester(meth)acrylate having a
cyclic alkyl group and ester(meth)acrylate having an aromatic hydrocarbon
group are preferable as the other copolymerizable monomer from the
standpoint of controlling elastic modulus of the pressure-sensitive
adhesive.

[0061] Particularly, in the acrylic polymer, the content of the sum of the
alkyl ester(meth)acrylate having a cyclic alkyl group and the
ester(meth)acrylate having an aromatic hydrocarbon group in the total
monomer component forming the acrylic polymer (100 wt %) is not
particularly limited, but is preferably 5 wt % to 50 wt %, and more
preferably 10 wt % to 40 wt %. If the content is more than 50 wt %, the
pressure-sensitive adhesive layer becomes hard, and there may be a
problem in that the adhesion property of the pressure-sensitive adhesive
sheet is decreased. Meanwhile, if the content is less than 5 wt %, (i) a
trace appears in the case where pressure is applied to the
pressure-sensitive adhesive layer. (ii) If pressure is applied to a
portion of the surface of the pressure-sensitive adhesive layer, there
may be a problem in that the portion to which the pressure is applied is
recessed, and then, the recessed portion is not recovered.

[0062] From the standpoint that the adhesion force to glass and the
relative dielectric constant of the pressure-sensitive adhesive sheet are
adjusted in a predetermined range, preferable embodiments of the monomer
components forming the acrylic polymer may include the following (a) to
(c).

Embodiment (a)

[0063] Alkoxyalkyl ester(meth)acrylate is used as the monomer component
forming the acrylic polymer, and the content of alkoxyalkyl
ester(meth)acrylate based on the total monomer component forming the
acrylic polymer (100 wt %) is 40 wt % or more (e.g., 40 wt % to 80 wt %),
and preferably 50 wt % or more (e.g., 50 wt % to 70 wt %).

Embodiment (b)

[0064] At least one copolymerizable monomer selected from the group
consisting of alkyl ester(meth)acrylate having a straight-chain or
branched alkyl group, alkyl ester(meth)acrylate having a cyclic alkyl
group, ester(meth)acrylate having an aromatic hydrocarbon group and
hydroxyl group-containing monomer is used as the monomer component
forming the acrylic polymer, and the content of the copolymerizable
monomer based on the total monomer component forming the acrylic polymer
(100 wt %) is 10 to 60 wt % (preferably 20 wt % to 40 wt %).

[0065] In the embodiment (b), the embodiment using alkoxyalkyl
ester(meth)acrylate as the monomer component forming the acrylic polymer
is not included.

Embodiment (c)

[0066] Alkoxyalkyl ester(meth)acrylate and hydroxyl group-containing
monomer are used as the monomer component forming the acrylic polymer,
and the content of alkoxyalkyl ester(meth)acrylate based on the total
monomer component forming the acrylic polymer (100 wt %) is 40 wt % or
more (e.g., 40 wt % to 80 wt %), and preferably 50 wt % or more (e.g., 50
to 70 wt %), and the content of the hydroxyl group-containing monomer
based on the total monomer component forming the acrylic polymer (100 wt
%) is 0.5 wt % to 50 wt % (preferably 1 wt % to 40 wt %).

[0067] The acrylic polymer is formed by polymerizing the above monomer
components by a known/general polymerization method. Examples of the
polymerization method include a solution polymerization method, an
emulsion polymerization method, a bulk polymerization method and a
polymerization method by active-energy-ray irradiation (an
active-energy-ray polymerization method or a photopolymerization method).
Among the above polymerization method, the solution polymerization method
and active-energy-ray polymerization method are preferable from the
standpoint of transparency, water resistance and costs, and particularly
when a relatively thick pressure-sensitive adhesive layer is formed, an
active-energy-ray polymerization method is preferable.

[0068] The active energy rays irradiated during the active-energy-ray
polymerization are not particularly limited, and examples thereof include
ultraviolet rays, or ionizing radiations such as an α-ray, a
β-ray, a γ-ray, a neutron ray, and an electron ray. Among
them, the ultraviolet rays are preferable as active energy rays.
Irradiation energy, irradiation time and irradiation method of active
energy rays used during the active-energy-ray polymerization are not
particularly limited as far as photopolymerization initiators as
described below can be activated to cause the reaction of monomer
components.

[0069] The solvent used in the solution polymerization is not particularly
limited, and various general solvents are used. Examples of the solvents
include organic solvents such as esters such as ethyl acetate and n-butyl
acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic
hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such
as cyclohexane and methylcyclohexane; ketones such as methyl ethyl ketone
and methyl isobutyl ketone. Such solvents are used either alone or in
combination of two or more thereof.

[0070] Polymerization initiators such as a photopolymerization initiator
or a thermal polymerization initiator are used depending on the type of
polymerization reaction in the formation of the acrylic polymer. The
polymerization initiators are used either alone or in combination of two
or more thereof.

[0073] Examples of the photoactive oxime-based photopolymerization
initiator include 1-phenyl-1,1-propandion-2-(o-ethoxycarbonyl)-oxime.
Examples of the benzoin-based photopolymerization initiator include
benzoin. Examples of the benzyl-based photopolymerization initiator
include benzyl. Examples of the benzophenone-based photopolymerization
initiator include benzophenone, benzoyl benzoate,
3,3'-dimethyl-4-methoxybenzophenone, polyvinyl benzophenone and
α-hydroxycyclohexyl phenylketone. Examples of the ketal-based
photopolymerization initiator include benzyl dimethyl ketal. Examples of
the thioxanthone-based photopolymerization initiator include
thioxanthone, 2-chlorothioxanthone, 2-methyl thioxanthone, 2,4-dimethyl
thioxanthone, isopropyl thioxanthone, 2,4-diisopropyl thioxanthone and
dodecyl thioxanthone. The photopolymerization initiators are used either
alone or in combination of two or more thereof.

[0074] The amount of the photopolymerization initiator used (particularly,
the content of the photopolymerization initiator in the acrylic
pressure-sensitive adhesive composition) is not particularly limited, but
it is preferably 0.005 to 1 part by weight and more preferably 0.01 to
0.5 part by weight based on 100 parts by weight of monomer components
forming an acrylic polymer.

[0075] The thermal polymerization initiator is not particularly limited,
and examples thereof include azo-based polymerization initiators,
peroxide-based polymerization initiators and redox-based polymerization
initiators. Examples of the azo-based polymerization initiators include
2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, dimethyl
2,2'-azobis(2-methylpropionate), 4,4'-azobis-4-cyanovaleric acid,
azobisisovaleronitrile, 2,2'-azobis(2-amidinopropan)dihydrochloride,
2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride,
2,2'-azobis(2-methylpropionamidine)disulfate and
2,2'-azobis(N,N'-dimethyleneisobutylamidine)dihydrochloride. Examples of
the peroxide-based polymerization initiators include dibenzoyl peroxide
and tert-butyl permaleate. The thermal polymerization initiators are used
either alone or in combination of two or more thereof. The amount of the
thermal polymerization initiator used is not particularly limited, and a
known range that can be used as a thermal polymerization initiator may be
used.

[0076] In the pressure-sensitive adhesive layer of the optical
pressure-sensitive adhesive sheet according to the present invention,
additives may be used as necessary within the amount ranges in which
characteristics of the present invention are not impaired. Examples of
the additives include crosslinking agents, crosslinking accelerators,
silane coupling agents, tackifiers (e.g., rosin derivative resin,
polyterpene resin, petroleum resin and oil soluble phenolic resin),
anti-aging agents, fillers, coloring agents (e.g., pigments and dyes),
ultraviolet absorbers, antioxidants, chain transfer agents, plasticizers,
softeners, surfactants and antistatic agents. The additives are used
either alone or in combination of two or more thereof.

[0077] Particularly, in the pressure-sensitive adhesive layer of the
optical pressure-sensitive adhesive sheet according to the present
invention, a silane coupling agent may be contained from the standpoint
of improving the adhesion property to optical members, particularly to
glass. The wording "the silane coupling agent is contained" includes a
case where the silane coupling agent is contained in the base polymer in
the pressure-sensitive adhesive layer as a constitutional unit as well as
a case where the silane coupling agent is contained in the
pressure-sensitive adhesive layer. The silane coupling agents are used
either alone or in combination of two or more thereof.

[0078] Namely, the optical pressure-sensitive adhesive sheet according to
the present invention may have the acrylic pressure-sensitive adhesive
layer containing the silane coupling agent.

[0079] The silane coupling agent is not particularly limited, and examples
thereof include γ-glycidoxypropyltrimethoxysilane,
γ-glycidoxypropyltriethoxysilane,
γ-aminopropyltrimethoxysilane and
N-phenyl-aminopropyltrimethoxysilane. Among them,
γ-glycidoxypropyltrimethoxysilane is preferable as the silane
coupling agent. Examples of the silane coupling agent may include
commercially available products such as trade name "KBM-403"
(manufactured by Shin-Etsu Chemical Co., Ltd.).

[0080] The content of the silane coupling agent in the pressure-sensitive
adhesive layer of the optical pressure-sensitive adhesive sheet according
to the present invention is not particularly limited. For example, in the
case where the pressure-sensitive adhesive layer of the optical
pressure-sensitive adhesive sheet according to the present invention is
the acrylic pressure-sensitive adhesive layer, the content of the silane
coupling agent in the acrylic pressure-sensitive adhesive layer is
preferably 0.01 to 2 parts by weight, and more preferably 0.05 to 0.8
parts by weight based on 100 parts by weight of the monomer component
forming the acrylic polymer.

[0081] In the pressure-sensitive adhesive layer of the optical
pressure-sensitive adhesive sheet according to the present invention, a
crosslinking agent is preferably used from the standpoint of improving
the adhesion property by increasing cohesion force of the
pressure-sensitive adhesive layer. The crosslinking agents are used
either alone or in combination of two or more thereof.

[0082] Namely, it is preferable that the optical pressure-sensitive
adhesive sheet according to the present invention has an acrylic
pressure-sensitive adhesive layer in which the crosslinking agent is
used. For example, it is preferable that the optical pressure-sensitive
adhesive sheet according to the present invention has the acrylic
pressure-sensitive adhesive layer formed from the acrylic
pressure-sensitive adhesive composition containing the crosslinking
agent. This is because that if the acrylic polymer is crosslinked by the
crosslinking agent, cohesion force of the pressure-sensitive adhesive
layer may be increased even more.

[0083] The crosslinking agent is not particularly limited, and for
example, in the case of the pressure-sensitive adhesive sheet having the
acrylic pressure-sensitive adhesive layer, it is preferable to use
isocyanate-based crosslinking agents or epoxy-based crosslinking agents
from the standpoint of improving the adhesion property to optical
members.

[0086] The content of the crosslinking agent in the pressure-sensitive
adhesive layer of the optical pressure-sensitive adhesive sheet according
to the present invention is not particularly limited. For example, in the
case of the pressure-sensitive adhesive sheet having the acrylic
pressure-sensitive adhesive layer, the content of the crosslinking agent
used in the acrylic pressure-sensitive adhesive layer is not particularly
limited, but preferably 0.001 to 20 parts by weight, and more preferably
0.01 to 10 parts by weight based on 100 parts by weight of the monomer
component forming the acrylic polymer.

[0087] The thickness of the pressure-sensitive adhesive of the optical
pressure-sensitive adhesive sheet according to the present invention is
not particularly limited, but is preferably 10 μm to 500 μM, and
more preferably 10 μm to 250 μm. The pressure-sensitive adhesive
may be a single layer structure or a laminate structure.

[0088] From the standpoint of increasing the adhesion force to glass to a
predetermined range, the crosslinking agent and/or silane coupling agent
may be used in the pressure-sensitive adhesive layer (particularly
acrylic pressure-sensitive adhesive layer) of the optical
pressure-sensitive adhesive sheet according to the present invention.
Particularly, in the case where the pressure-sensitive adhesive layer of
the pressure-sensitive adhesive sheet according to the present invention
is the acrylic pressure-sensitive adhesive layer, the crosslinking agent
such as the epoxy-based crosslinking agent or isocyanate-based
crosslinking agent and/or silane coupling agent may be used in the
acrylic pressure-sensitive adhesive layer. For example, the
pressure-sensitive adhesive sheet according to the present invention may
have the acrylic pressure-sensitive adhesive layer formed from the
acrylic pressure-sensitive adhesive composition containing the
crosslinking agent and/or silane coupling agent.

[0089] (Substrate)

[0090] In the case where the optical pressure-sensitive adhesive sheet
according to the present invention is a pressure-sensitive adhesive sheet
with substrate, the substrate is not particularly limited, and examples
of the substrate include various kinds of optical films such as a plastic
film, an anti-reflective (AR) film, a polarizer and a retardation film.
Examples of materials of the plastic film include plastics materials such
as polyester-based resins such as polyethylene terephthalate (PET),
acrylic resins such as polymethylmethacrylate (PMMA), polycarbanate,
triacetylcelluous, polysulfone, polyarylate and cyclic olefin based
polymers such as cyclic olefin based polymer with trade name of `ARTON`
manufactured by JSR Corporation and cyclic olefin based polymer with
trade name of `ZEONOR` manufactured by ZEON Corporation. The plastic
materials are used either alone or in combination of two or more thereof.
The `substrate` is a portion laminated to an adherend together with the
pressure-sensitive adhesive layer, when the optical pressure-sensitive
adhesive sheet is used (laminated) to the adherend (optical member). The
release liner (separator) to be described below which is released in the
use (lamination) of the optical pressure-sensitive adhesive sheet is not
included in the `substrate`.

[0091] As the substrate, among them, a transparent substrate is preferable
from the standpoint of achieving high transparency in the
pressure-sensitive adhesive sheet. The `transparent substrate` is
preferably a substrate having a total light transmittance of 85% or more
in a visible light wavelength range in accordance with JIS K 7361, and
more preferably a substrate having a total light transmittance of 90% or
more. Examples of the transparent substrate include a PET film, and
non-oriented films such as trade names of `ARTON` and `ZEONOR`.

[0092] A thickness of the substrate is not particularly limited, but is
preferably 12 μm to 50 μm. The substrate may be formed in any forms
of a single layer or plural layers. Proper known/general surface
treatment such as corona discharge treatment, physical treatment such as
plasma treatment, and chemical treatment such as base coating treatment
may be performed on the surface of the substrate.

[0093] The substrate may be an optical member. That is, the optical
pressure-sensitive adhesive sheet according to the present invention may
be constituted by a substrate formed of an optical member and a
pressure-sensitive adhesive layer.

[0094] (Release Liner)

[0095] The pressure-sensitive adhesive surfaces of the optical
pressure-sensitive adhesive sheet according to the present invention may
be protected by a release liner until they are used. The respective
pressure-sensitive adhesive surfaces of the optical pressure-sensitive
adhesive sheet may be protected by two release liners, respectively, or
may be protected in a roll-shape wound form by a release liner of which
both sides are formed as release faces. The release liner is used as
protecting material of the pressure-sensitive adhesive layer, and is
released when it is laminated to an adherend. In the case where the
optical pressure-sensitive adhesive sheet according to the present
invention is a substrateless double-sided pressure-sensitive adhesive
sheet, the release liner also acts as a support of the pressure-sensitive
adhesive layer. The release liner may be optionally provided.

[0096] Such a release liner is not particularly limited, and examples
thereof include a general release paper, a substrate with a
release-treated layer, a low adhesion substrate made of a fluorine-based
polymer and a low adhesion substrate made of a non-polar polymer.
Examples of the substrate with the release-treated layer include plastic
films or papers of which surfaces are treated by release treating agents
such as a silicone-based release treating agent, a long chain alkyl-based
release treating agent, fluorine-based release treating agent, and
molybdenum sulfate. Examples of the fluorine-based polymer of a low
adhesion substrate made of a fluorine-based polymer include
polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride,
polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene
copolymer and chlorofluoroethylene-vinylidene fluoride copolymer.

[0097] Examples of the non-polar polymer of a low adhesion substrate made
of a non-polar polymer include olefin-based resins such as polyethylene
and polypropylene. The release liner may be formed by know/general
methods. The thickness of the release liner are not particularly limited.

[0098] (Optical Pressure-Sensitive Adhesive Sheet)

[0099] A method for manufacturing the optical pressure-sensitive adhesive
sheet according to the present invention is not particularly limited, but
known/general methods are used. For example, the substrateless type
pressure-sensitive adhesive sheet is manufactured by forming the
pressure-sensitive adhesive layer on a release-treated layer of the
release liner, and the pressure-sensitive adhesive sheet with the
substrate is manufactured by forming the pressure-sensitive adhesive
layer on the substrate or transferring the separately formed
pressure-sensitive adhesive layer on the substrate.

[0100] A method for forming a pressure-sensitive adhesive layer when the
optical pressure-sensitive adhesive sheet according to the present
invention is formed is not particularly limited, and the
pressure-sensitive adhesive layer may be formed by known/general methods
for forming pressure-sensitive adhesive layer. The methods for forming
the pressure-sensitive adhesive layer vary depending on polymerization
methods of a base polymer, and examples thereof may include the following
methods.

[0101] (1) A pressure-sensitive adhesive layer is formed by coating on a
substrate or release liner a composition (a pressure-sensitive adhesive
composition or active-energy-ray curable pressure-sensitive adhesive
composition) containing a mixture of monomer components (monomer mixture)
forming a base polymer or a partially polymerized product thereof, and
additives such as a photopolymerization initiator added as necessary, and
irradiating active energy rays thereon.

[0102] (2) A pressure-sensitive adhesive layer is formed by coating on a
substrate or release liner a composition (a pressure-sensitive adhesive
composition or solvent type pressure-sensitive adhesive composition)
containing a base polymer, solvent and additives added as necessary, and
drying and/or curing the composition.

[0103] Heating and drying steps may be performed in methods (1) and (2) if
necessary. The `monomer mixture` means a mixture consisting of monomer
components forming a base polymer. The `partially polymerized product
thereof` means a composition in which one or more of the components in
the monomer mixture are partially polymerized.

[0104] In the methods for forming the pressure-sensitive adhesive layer,
coating of the pressure-sensitive adhesive composition may be performed
by using any known coating methods. For example, the pressure-sensitive
adhesive composition may be coated on the substrate or release liner by
using coaters such as a gravure roll coater, a reverse roll coater, a
kiss roll coater, a dip roll coater, a bar coater, a knife coater, a
spray coater, a comma coater and a direct coater.

[0105] In the present invention, for example, the optical
pressure-sensitive adhesive sheet (optical acrylic pressure-sensitive
adhesive sheet) having the acrylic pressure-sensitive adhesive layer is
manufactured by the following manufacturing method 1 or manufacturing
method 2.

[0106] Manufacturing method 1: Manufacturing method for obtaining a
pressure-sensitive adhesive sheet, including forming a pressure-sensitive
adhesive composition layer by coating on a predetermined surface of a
release liner a pressure-sensitive adhesive composition containing a
mixture of monomer components forming an acrylic polymer (acrylic monomer
mixture) or a partially polymerized product thereof and a
photopolymerization initiator, and then curing the pressure-sensitive
adhesive composition layer by an active-energy-ray irradiation to form an
acrylic pressure-sensitive adhesive layer.

[0107] Manufacturing method 2: Manufacturing method for obtaining a
pressure-sensitive adhesive sheet, including coating a pressure-sensitive
adhesive composition containing an acrylic polymer and solvent on a
predetermined surface of a release liner to form a pressure-sensitive
adhesive composition layer, and then, drying and/or curing the
pressure-sensitive adhesive composition to form an acrylic
pressure-sensitive adhesive layer.

[0108] From the standpoint of setting the adhesion force to glass and
relative dielectric constant of the pressure-sensitive adhesive sheet
within a predetermined range, it is preferable that the monomer component
forming the acrylic polymer as described in the above embodiments (a) to
(c), which are preferable embodiments of the monomer component forming
the acrylic polymer, are preferably used in preparing the acrylic
pressure-sensitive adhesive composition of manufacturing method 1 and
manufacturing method 2.

[0109] The thickness of the optical pressure-sensitive adhesive sheet
according to the present invention is not particularly limited, but is
preferably 10 μm to 500 μm, and more preferably 10 μm to 250
μm.

[0110] Since the optical pressure-sensitive adhesive sheet according to
the present invention has the adhesion force to glass within a
predetermined range, the excellent adhesion property to the optical
member is exhibited, and particularly, the excellent adhesion property to
optical members made of glass is exhibited. Since the optical
pressure-sensitive adhesive sheet according to the present invention has
a relative dielectric constant at a frequency of 1 MHz within a
predetermined range, functions or characteristics of the optical members
are not damaged when the optical pressure-sensitive adhesive sheet is
applied to the optical members. Particularly, the optical
pressure-sensitive adhesive sheet according to the present invention
exhibits an excellent adhesion property to the members constituting the
touch panel and the performances such as a detection sensitivity or
response speed of the touch panel are not negatively affected, when used
for laminating members constituting the electric capacity type touch
panel.

[0111] The optical members refer to members having optical properties such
as a polarized property, a photorefractivity property, a light scattering
property, a light reflective property, a light transmitting property, a
light absorbing property, a light diffractive property, an optical
rotation property and visibility. Although the optical members are not
particularly limited as far as they are members having optical
properties, examples thereof include members constituting devices
(optical devices) such as display devices (image display devices) and
input devices, or members used in the devices. Examples of the optical
members include a polarizing plate, a wave plate, a retardation plate, an
optical compensation film, a brightness enhancing film, a light guide
plate, a reflective film, an anti-reflective film, a transparent
conductive film (ITO film), a design film, a decoration film, a surface
protection film, a prism, lens, a color filter, a transparent substrate,
and members in which these are laminated. The `plate` and `film` include
plate form, film form and sheet form, and examples of the `polarizing
plate` include `a polarizing film` and `a polarizing sheet`.

[0112] Examples of the display devices include a liquid crystal display,
an organic electroluminescence (EL) display device, a Plasma Display
Panel (PDP) and an electronic paper. Examples of the input devices
include touch panels, particularly, such as an electric capacity type
touch panel.

[0113] The optical pressure-sensitive adhesive sheet according to the
present invention is preferably used for the purpose of laminating
members constituting the electric capacity type touch panel.

[0114] The optical members are not particularly limited, and examples
thereof include members (e.g., a sheet, film or plate type of members)
formed of an acrylic resin, polycarbonate, polyethylene terephthalate,
glass and metal films. The `optical members` in the present invention may
include members paying a role of decoration or protection while
maintaining visibility of a display device or input device that is an
adherent as described above (a design film, a decorating film and a
surface protection film).

[0115] Although embodiments of laminating optical members by the optical
pressure-sensitive adhesive sheet according to the present invention are
not particularly limited, they may include (1) an embodiment of
interposing the pressure-sensitive adhesive sheet between the optical
members to laminate the optical members to each other, (2) an embodiment
of laminating an optical member to any members other than the optical
member through the pressure-sensitive adhesive sheet, and (3) an
embodiment of laminating the pressure-sensitive adhesive sheet including
the optical member to optical members or any members other than the
optical members. In the above embodiment (3), it is preferable that the
pressure-sensitive adhesive sheet is a pressure-sensitive adhesive sheet
with substrate using an optical member such as a polarizing film and an
optical film as a substrate.

[0116] A pressure-sensitive adhesive type optical member having the
pressure-sensitive adhesive layer on at least one surface of the optical
member may be obtained by adhering and laminating the optical
pressure-sensitive adhesive sheet (particularly, substrateless type)
according to the present invention on the surface (at least one surface)
of the optical member.

[0117] As a more specific example, FIG. 1 shows a schematic view
illustrating an embodiment of an electric capacity type touch panel
formed by laminating members using an optical pressure-sensitive adhesive
sheet according to the present invention. In FIG. 1, reference numeral 1
represents an electric capacity type touch panel, reference numeral 11
represents a transparent protective lens, reference numeral 12 represents
an optical pressure-sensitive adhesive sheet, reference numeral 13a
represents an ITO glass substrate, reference numeral 13b represents an
ITO film (transparent conductive film), and reference numeral 14
represents a liquid crystal display. In the electric capacity type touch
panel 1, the "transparent protective lens 11" and the "ITO glass
substrate 13a, on both sides of which the ITO films 13b are coated" are
laminated through the optical pressure-sensitive adhesive sheet 12, and
the "ITO glass substrate 13a, on both sides of which the ITO films 13b
are coated" and the "liquid crystal display 14" are laminated through the
optical pressure-sensitive adhesive sheet 12. In the electric capacity
type touch panel 1, one in which the ITO film 13b is coated on both
surfaces of the ITO glass substrate 13a is used, but in general, in the
electric capacity type touch panel, one in which the ITO film is coated
on one surface of the ITO glass substrate may be used. It is preferable
that the transparent protective lens 11 is a transparent protective lens
made of glass or plastic. It is also preferable that the surface layer of
the liquid crystal display 14 is a glass layer or a plastic film layer.

[0118] In the electric capacity type touch panel in which the optical
pressure-sensitive adhesive sheet according to the present invention is
used, such as the electric capacity type touch panel 1, the
pressure-sensitive adhesive sheet has excellent adhesion property to the
members constituting the touch panel, particularly to the members of
which the surface is made of glass. Accordingly, releasing does not occur
between the members during using the touch panel. Further, in the
electric capacity type touch panel in which the pressure-sensitive
adhesive sheet according to the present invention is used, the relative
dielectric constant of the pressure-sensitive adhesive sheet at a
frequency of 1 MHz is in a predetermined range. Therefore, the detection
sensitivity or response speed is excellent, and noise is difficult to be
detected. Accordingly, the electric capacity type touch panel in which
the optical pressure-sensitive adhesive sheet according to the present
invention is used has an excellent operation stability. In the electric
capacity type touch panel in which the pressure-sensitive adhesive sheet
according to the present invention is used, the visibility is also
excellent if the transparency of the pressure-sensitive adhesive sheet is
high.

[0119] (Optical Device)

[0120] By using the optical pressure-sensitive adhesive sheet when
laminating members constituting optical devices or members used in the
devices, the optical device in which the optical pressure-sensitive
adhesive sheet is used may be obtained.

[0121] Examples of the optical device include a liquid crystal display
device, an organic EL display device, a PDP, a display device (image
display device) such as an electronic paper, and an input device such as
a touch panel (particularly, electric capacity type touch panel).

[0122] Since the optical pressure-sensitive adhesive sheet is used in the
optical device, the detection sensitivity or response speed is good,
noise is difficult to be detected, and the operation stability is
excellent. If the transparency of the pressure-sensitive adhesive sheet
is high, the visibility is also excellent.

EXAMPLES

[0123] Hereinafter, the present invention will be described in more detail
with reference to the following Examples, but the present invention is
not limited to the following Examples.

Example 1

[0124] 55 parts by weight of methoxyethyl acrylate (MEA), 12 parts by
weight of ethylacrylate (EA), 15 parts by weight of methylmeth acrylate
(MMA), 18 parts by weight of 4-hydroxybutyl acrylate (4HBA), 0.3 parts by
weight of azobisisobutyronitrile and 233.8 parts by weight of ethyl
acetate as a polymerization solvent were placed into a separable flask,
followed by agitating for 1 hour while introducing nitrogen gas
thereinto. Then, oxygen was removed from the polymerization system, and
the polymerization system was heated to 63° C., followed by
reacting for 10 hours to obtain an acrylic polymer solution having a
solid concentration of 30 wt %. The acrylic polymer in the acrylic
polymer solution had a weight average molecule weight of 1,100,000.

[0126] This solution was coated on the release-treated surface of the
release liner (release liner in which one side of the
polyethyleneterephthalate film was release-treated, thickness of 38
μm, trade name "MRF38", manufactured by Mitsubishi Plastics Inc.) to
form a coat layer, and the coat layer was heated and dried at 60°
C. for 30 sec and at 150° C. for 1 min, followed by further aging
at 23° C. for 120 hours to prepare a pressure-sensitive adhesive
sheet (substrateless type, the thickness of the pressure-sensitive
adhesive layer: 50 μm).

[0127] The same release liner was provided on the pressure-sensitive
adhesive surface opposite to the pressure-sensitive adhesive surface on
which the release liner was provided.

Example 2

[0128] 67 parts by weight of butyl acrylate (BA), 14 parts by weight of
cyclohexyl acrylate (CHA), 27 parts by weight of 4-hydroxybutyl acrylate
(4HBA), 9 parts by weight of hydroxyethyl acrylate (HEA), 0.05 parts by
weight of 2,2-dimethoxy-1,2-diphenyl-1-one (trade name "IRGACURE 651",
manufactured by BASF Japan Co., Ltd.) and 0.05 parts by weight of
1-hydroxy-cyclohexyl-phenyl-ketone (trade name "IRGACURE 184",
manufactured by BASF Japan Co., Ltd.) were placed into a four-neck flask,
and the mixture was partially photopolymerized by exposing to UV under
the nitrogen atmosphere to obtain a partially polymerized product
(monomer syrup) having the polymerization ratio of 10%.

[0130] This photopolymerizable composition was coated on the
release-treated surface of the release liner (release liner in which one
side of the polyethylene terephthalate film was release-treated,
thickness of 38 μm, trade name "MRF38", manufactured by Mitsubishi
Plastics Inc.) to form a coat layer, and then, the same release liner was
provided on the coat layer.

[0131] Next, the pressure-sensitive adhesive sheet (substrateless type,
the thickness of the pressure-sensitive adhesive layer: 175 μm) was
prepared by irradiating UV having the intensity of 5 mW/cm2 by the
black light and performing polymerization until the light intensity of
3600 mJ/cm2 was irradiated thereon.

[0132] The weight average molecule weight of the acrylic polymer as the
base polymer of the pressure-sensitive adhesive layer was 2,000,000.

Example 3

[0133] The pressure-sensitive adhesive sheet was prepared in the same
manner as in Example 1, except that the monomer components were 66 parts
by weight of methoxyethyl acrylate (MEA), 1 parts by weight of
4-hydroxybutyl acrylate (4HBA), 23 parts by weight of ethyl acrylate (EA)
and 10 parts by weight of methyl methacrylate (MMA). Similar to Example
1, the release liner was provided on the adhesion surface opposite to the
pressure-sensitive adhesive surface on which the release liner was
provided.

[0134] The acrylic polymer in the acrylic polymer solution had a weight
average molecule weight of 1,000,000.

Example 4

[0135] The pressure-sensitive adhesive sheet was prepared in the same
manner as in Example 1, except that the monomer components were 59 parts
by weight of methoxyethyl acrylate (MEA), 40 parts by weight of
2-ethylhexyl acrylate (2EHA) and 1 part by weight of 4-hydroxybutyl
acrylate (4HBA). Similar to Example 1, the release liner was provided on
the pressure-sensitive adhesive surface opposite to the
pressure-sensitive adhesive surface on which the release liner was
provided.

[0136] The acrylic polymer in the acrylic polymer solution had a weight
average molecule weight of 1,000,000.

Comparative Example 1

[0137] The pressure-sensitive adhesive sheet was prepared in the same
manner as in Example 2, except that the monomer components were 88 parts
by weight of isooctyl acrylate (iOA) and 12 parts by weight of acrylic
acid (AA).

[0138] The weight average molecule weight of the acrylic polymer as the
base polymer of the pressure-sensitive adhesive layer was 1,000,000.

Comparative Example 2

[0139] The pressure-sensitive adhesive sheet was prepared in the same
manner as in Example 2, except that the monomer components were 95 parts
by weight of butyl acrylate (BA) and 5 parts by weight of acrylic acid
(AA).

[0140] The weight average molecule weight of the acrylic polymer as the
base polymer of the pressure-sensitive adhesive layer was 800,000.

Comparative Example 3

[0141] The pressure-sensitive adhesive sheet was prepared in the same
manner as in Example 2, except that the monomer components were 99 parts
by weight of butyl acrylate (BA) and 1 parts by weight of 4-hydroxybutyl
acrylate (4HBA).

[0142] The weight average molecule weight of the acrylic polymer as the
base polymer of the pressure-sensitive adhesive layer was 800,000.

[0143] (Evaluation)

[0144] The relative dielectric constant, adhesion strength to glass
(adhesion force to glass), total light transmittance and haze were
measured with respect to the pressure-sensitive adhesive sheet in the
Examples and Comparative Examples. The measurement results were shown in
Table 1.

[0145] (Relative Dielectric Constant)

[0146] The relative dielectric constant at the frequency of 1 MHz was
measured under the following condition in accordance with JIS K 6911.

[0148] Electrode constitution: Aluminum plate having a diameter of 12.1 mm
and the thickness of 0.5 mm

[0149] Counter electrode: 3 oz copper plate

[0150] Measurement environment: 23±1° C., 52±1% RH

[0151] (Adhesion Strength to Glass)

[0152] The specimen was prepared by cutting the pressure-sensitive
adhesive sheet into the size of width 20 mm×length 100 mm, exposing
the pressure-sensitive adhesive surface by releasing one release liner of
the cut pressure-sensitive adhesive sheet, and laminating the PET film
(backing material) having the thickness of 25 μm to the
pressure-sensitive adhesive surface.

[0153] Then, the pressure-sensitive adhesive surface was exposed by
releasing the release liner of the specimen, and the specimen in which
the pressure-sensitive adhesive surface was exposed were laminated to a
glass plate (slide glass, No. "S-1111", Matsunami Glass Industry Co.,
Ltd.) by pressing by moving a roller of 2 kg (width: about 50 mm) back
and forth once. The specimen and glass plate were left standing for 30
min after laminating. The adherend surface of the glass plate was the
surface from which fluorescence was not emitted even when UV having the
wavelength of 254 nm was irradiated by a UV lamp.

[0154] Next, the release adhesion strength to glass (adhesion force to
glass) (N/20 mm) was measured by releasing the specimen from the glass
plate under the environment of 23° C. and 50% RH by using the
tensile tester under the condition of the release angle of 180°
and the tensile speed of 300 mm/min.

[0155] (Total Light Transmittance and Haze)

[0156] The pressure-sensitive adhesive surface was exposed by releasing
one release liner of the pressure-sensitive adhesive sheet (the layer
structure of the release liner/pressure-sensitive adhesive layer/release
liner), and the pressure-sensitive adhesive sheet in which the
pressure-sensitive adhesive surface was exposed was laminated to the
glass plate (slide glass, No. "S-1111", Matsunami Glass Industry Co.,
Ltd.). The measurement sample having the layer structure of the glass
plate/pressure-sensitive adhesive layer was prepared by releasing the
other release liner.

[0157] With respect to the sample for measurement, the total light
transmittance and haze were measured by the haze meter (device name
`HM-150` manufactured by Murakami Color Research Laboratory Co., Ltd.).
The haze (%) was obtained by the equation of "diffusion
transmittance/total light transmittance×100".

[0158] While the invention has been described in detail and with reference
to specific embodiments thereof, it will be apparent to one skilled in
the art that various changes and modifications can be made therein
without departing from the spirit and scope thereof.

[0159] This application is based on Japanese Patent Application No.
2010-278847 filed on Dec. 15, 2010, and the entire subject matter of
which is incorporated herein by reference.

[0161] (1) An optical pressure-sensitive adhesive sheet comprising a
pressure-sensitive adhesive layer, wherein a relative dielectric constant
at a frequency of 1 MHz is 5 to 10, and an adhesion strength to a glass,
which is measured with a peel angle of 180° and a tensile speed of
300 mm/min after 30 min of laminating the optical pressure-sensitive
adhesive sheet to the glass, is 3 N/20 mm to 15 N/20 mm.

[0163] (3) The optical pressure-sensitive adhesive sheet according to (2),
wherein the acrylic pressure-sensitive adhesive layer comprises, as a
base polymer, an acrylic polymer formed from a component comprising, as
an essential monomer component, alkyl ester(meth)acrylate having a
straight-chain or branched alkyl group having 1 to 14 carbon atoms and/or
alkoxyalkyl ester(meth)acrylate.

[0164] (4) The optical pressure-sensitive adhesive sheet according to (3),
wherein the acrylic polymer is formed by an active-energy-ray
polymerization method with an irradiation of an active-energy-ray.

[0165] (5) The optical pressure-sensitive adhesive sheet according to any
one of (1) to (4), wherein the pressure-sensitive adhesive layer
comprises a silane coupling agent.

[0166] (6) The optical pressure-sensitive adhesive sheet according to any
one of (1) to (5), which has a total light transmittance of 90% or more
and a haze of 3.0% or less.

[0167] (7) The optical pressure-sensitive adhesive sheet according to any
one of (1) to (6), which is used for laminating to a member contained in
a touch panel.